Technical Sharing: How to Control the Thickness of Electrostatic Powder Coating
Spray-painted profiles come in a variety of colors and are deeply loved by a wide range of customers. However, due to the complexity of the cross-sectional shapes of aluminum profiles, it brings certain difficulties to the spraying production and coating thickness inspection. Regardless of the shape of the aluminum profile, the minimum local film thickness of the coating on its decorative surface should be ≥40um. This is a mandatory implementation clause stipulated in GB5237.4-2008 and must be strictly adhered to and executed. Other areas such as the inner corners, transverse grooves and slots are allowed to be less than the thickness of the coating film, but the base layer must not be exposed.
In actual production, due to the influence of electrostatic spraying equipment and the cross-sectional shape of aluminum profiles, there are certain requirements for the accurate control of coating thickness. The characteristics of the spraying production line can be better controlled in terms of coating thickness from the following aspects.
1.SUSPENSION WEY
Selecting the appropriate hangers based on the shape of the aluminum profiles and choosing the correct hanging method is the key to controlling the thickness of the coating. It not only improves the quality of the coating on the aluminum profiles but also reduces the workload of the powder room operators in manually patting powder with a gun. Especially, the spacing of the hanging materials can adjust the thickness of the powder coating. The general requirement for the spacing of the hanging materials is: the width of the aluminum profile = the spacing of the aluminum profiles.
2.The workpiece comes into contact with the hanger
Due to poor contact between the workpiece and the hanger (i.e., poor conductivity), it will seriously affect the coating efficiency and the quality of the coating, resulting in a low powder coating rate on the workpiece and causing the coating film thickness to be low or even exposed. It also puts a lot of pressure on the recovery system, causing the excess powder to overflow outside the powder room in time, which not only reduces the utilization rate of the powder but also pollutes the environment.
When the workpieces have poor contact, the coating thickness of the products produced at different points on the same piece of material may differ by 30um to 70um. In some areas, due to the overly thick coating, defects such as orange peel, pinholes, and flow marks may occur, and the color and gloss will also be affected. Moreover, under natural light, the sand-textured powder profiles can be visually inspected to show obvious defects such as zebra lines. Therefore, it is essential to ensure good electrical conductivity between the workpiece and the hanger.
3．Conveyor chain speed and production process
在生产时输送链条的速度以及生产工艺对粉末喷涂涂层的厚度起着主要的作用，如：升降机的行程，枪距，粉压，静电电压等，升降机行程的高度一般要求是：行程高度=工件高度+200㎜。工件形状越复杂，喷枪与工件距离越近，要求出粉量越小，电压越低；反之，工件形状越简单，喷枪与工件距离越远，出粉量越大，电压越高。
4．The way to replenish powder with a hand spray gun
Due to the complexity of the cross-sectional shape of aluminum profiles, during the production process, the inner corners, transverse grooves, and slots used as decorative surfaces are areas that are difficult for automatic spray guns to reach. Therefore, manual spray guns must be used for supplementary spraying. When the nozzle of the manual spray gun is pointed at the area to be re-sprayed on the workpiece, the powder conveying pressure is adjusted too much, or the distance between the manual spray gun and the workpiece is too close, All of these can easily cause phenomena such as orange peel, flow marks, pinholes, gun marks and fat edges on the surface of the workpiece. Under normal circumstances, when the nozzle of the hand spray gun is directly facing the area to be sprayed on the workpiece, the distance between the hand spray gun and the workpiece should be controlled at about 80 to 150mm.
5.Powder pump factor
The common uneven powder output during the production process is mainly caused by the unclean Venturi powder pump part. Due to the fast spray speed of the powder pump, it is easy to cause collision and melting inside the powder pipe, as well as powder adhesion, leading to blockage. This will affect the two-phase flow of powder and gas in the powder pipe, thereby affecting the coating thickness of the workpiece. Under normal circumstances, the operators in the powder room should promptly check the cleanliness of all parts of the Venturi powder pump.
Disclaimer: The content of this article is reprinted from Aluminum Plus Network. The copyright belongs to the original author. The purpose of reprinting is to convey more information, and it does not mean that this website agrees with its views or is responsible for its authenticity. If there are any issues related to the content, copyright or other problems, please contact us by phone or letter and we will handle them promptly!
